Image forming apparatus such as copiers, facsimiles and printers forms an invisible electro-static image on a photoconductive drum, which is an image carrier, by scanning its surface with semiconductor laser, for example, laser beams emitted from a laser diode, and prints the invisible electrostatic image onto paper to make it visible by the use of a developing agent (toner).
The laser beam emitted from a laser diode hits a galvanometer mirror to be reflected there and then proceeds to a polygon mirror. The laser beam, reflected by the polygon mirror, scans the surface of a photoconductive drum along the axis of the drum, driven by rotational movements of the polygon mirror. This scanning performed along the drum axis is referred to as main scanning. The main scanning is repeated, driven by the rotating photoconductive drum. The direction of the shift of repeated main scanning conducted on the photoconductive drum (perpendicular to the direction of the main scanning) is referred to as sub-scanning direction. The position of the laser beam irradiation in the sub-scanning direction is adjusted by the galvanometer mirror.
In such image forming apparatus, if a user switches off the machine by mistake, the power line is unplugged, or the commercial power service fails, the process including image formation is interrupted. In such cases, the data under use for the control of image formation has to be saved on a non-volatile memory so as not to be lost. Furthermore, after the data has been saved, a process is required that prohibits access to the non-volatile memory to protect the data saved in the non-volatile memory.
Although it is the control unit of the apparatus that conducts this process, the power supply to this control unit has also been cut off when it is supposed to carry out such a process. For the implementation of this process, the power required to continue operation must be set aside somewhere in advance to be ready for use by the control unit.
As a means for storing power for operation, a capacitor for power smoothing may be used in the power supply circuit of the apparatus.
The power supply circuit includes a transformer that transforms the source AC voltage, a regulator circuit that regulates the secondary voltage of this transformer, and a capacitor for smoothing the output DC voltage provided from the regulator circuit. In the power smoothing capacitor, charge remains for a short time after the power supply has failed. This residual charge can make the control unit continue its operation even after the stop of power supply.
However, the capacity of common power smoothing capacitors is not high enough to ensure the completion of the above process.
To complete the above process, a capacitor of a great capacity has to be employed as the power smoothing capacitor. However, the use of such a smoothing capacitor of a large capacity leads to a larger power supply circuit. In addition, there is another disadvantage that such a capacitor of a large capacity is expensive.
It is, therefore, the object of the present invention to provide a power supplying apparatus, an image forming apparatus and method of controlling the same those can ensure the completion of the necessary process in case of the shutoff of power supply without employing a power smoothing capacitor of a high capacity.
The power supplying apparatus according to this invention has a power supply circuit that transforms the AC voltage into DC voltage; a motor that operates powered by the output of the power supply circuit and continues to run by inertial rotation even after loss of the output; at least one non-volatile memory for data saving; and a control unit that operates powered by the output of the power supply circuit, operates powered by the voltage generated in the motor rotating by inertia, saves the data that has been used for controlling when the output voltage of the power supply circuit decreases and then prohibits access to the non-volatile memory after the data saving.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.